Local liquid holdups and hysteresis in a 2-D packed bed using X-ray radiography

An X-ray visualization technique has been used for the quantitative determination of local liquid holdups distribution and liquid holdup hysteresis in a nonwetting two-dimensional (2-D) packed bed. A medical diagnostic X-ray unit has been used to image the local holdups in a 2-D cold model having a random packing of expanded polystyrene beads. An aqueous barium chloride solution was used as a fluid to achieve good contrast on X-ray images. To quantify the local liquid holdup, a simple calibration technique has been developed that can be used for most of the radiological methods such as gamma ray and neutron radiography. The global value of total liquid holdup, obtained by X-ray method, has been compared with two conventional methods: drainage and tracer response. The X-ray technique, after validation, has been used to visualize and quantify, the liquid hysteresis phenomena in a packed bed. The liquid flows in preferred paths or channels that carry droplets/rivulets of increasing size and number as the liquid flow rate is increased. When the flow is reduced, these paths are retained and the higher liquid holdup that persists in these regions leads to the holdup hysteresis effect. Holdup in some regions of the packed bed may be an order of magnitude higher than average at a particular flow rate. (c) 2005 American Institute of Chemical Engineers

Narrowing of the inferior dental canal in relation to the lower third molars

Objectives: To assess narrowing of the inferior dental canal in the lower third molar regions using computed tomography (CT) and to determine the value of radiographic markers on rotational panoramic radiographs in assessing the true relationships of the inferior dental canal. Methods: Patients referred for CT assessment of impacted lower third molars were used in this study. The lower third molars were assessed using CT to determine the position and morphology of the inferior dental canal relative to the roots and the cortical plates. The radiographic markers on rotational panoramic radiographs were correlated with the CT findings when rotational panoramic radiographs were available. Results: The patients referred had 202 lower third molars. Inferior positioning of the inferior dental canal was the most common location on CT. Narrowing of the inferior dental canal was found in relation to the lower third molars in 66.8% of cases. The chance of narrowing of the inferior dental canal as shown using CT increased when at least one of the radiographic markers, superimposition, narrowing, deviation or reduction in density was present on the rotational panoramic radiograph. Deviation of the inferior dental canal on rotational panoramic radiographs was found to be the most significant predictor of narrowing of the inferior dental canal and a close relationship to the roots, as shown in CT. Conclusions: Narrowing of the inferior dental canal is a common finding when impacted lower third molars are assessed using CT. On rotational panoramic radiographs deviation of the inferior dental canal is the best predictor of narrowing of the inferior dental canal and a close relationship to the roots.

Cell death mechanisms associated with G(2) radiosensitivity in patients with prostate cancer and benign prostatic hyperplasia

Cells respond to genotoxic insults such as ionizing radiation by halting in the G(2) phase of the cell cycle. Delayed cell death (mitotic death) can occur when the cell is released from G(2), and specific spindle defects form endopolyploid cells (endoreduplication/tetraploidy). Enhanced G(2) chromosomal radiosensitivity has been observed in many cancers and genomic instability syndromes, and it is manifested by radiation-induced chromatid aberrations observed in lymphocytes of patients. Here we compare the G(2) chromosomal radiosensitivity in prostate patients with benign prostatic hyperplasia (BPH) or prostate cancer with disease-free controls. We also investigated whether there is a correlation between G(2) chromosomal radiosensitivity and aneuploidy (tetraploidy and endoreduplication), which are indicative of mitotic cell death. The G(2) assay was carried out on all human blood samples. Metaphase analysis was conducted on the harvested chromosomes by counting the number of aberrations and the mitotic errors (endoreduplication/tetraploidy) separately per 100 metaphases. A total of 1/14 of the controls were radiosensitive in G(2) compared to 6/15 of the BPH patients and 15/17 of the prostate cancer patients. Radiation-induced mitotic inhibition was assessed to determine the efficacy of G(2) checkpoint control in the prostate patients. There was no significant correlation of G(2) radiosensitivity scores and mitotic inhibition in BPH patients (P = 0.057), in contrast to prostate cancer patients, who showed a small but significant positive correlation (P = 0.029). Furthermore, there was no significant correlation between G(2) radiosensitivity scores of BPH patients and endoreduplication/ tetraploidy (P = 0.136), which contrasted with an extremely significant correlation observed in prostate cancer patients (P < 0.0001). In conclusion, cells from prostate cancer patients show increased sensitivity to the induction of G(2) aberrations from ionizing radiation exposure but paradoxically show reduced mitotic indices and aneuploidy as a function of aberration frequency.

The effect of introducing radiographer reporting on the availability of reports for Accident and Emergency and General Practitioner examinations: a time-series analysis

This study explores whether the introduction of selectively trained radiographers reporting Accident and Emergency (A&E) X-ray examinations or the appendicular skeleton affected the availability of reports for A&E and General Practitioner (GP) examinations at it typical district general hospital. This was achieved by analysing monthly data on A&E and GP examinations for 1993 1997 using structural time-series models. Parameters to capture stochastic seasonal effects and stochastic time trends were included ill the models. The main outcome measures were changes in the number, proportion and timeliness of A&E and GP examinations reported. Radiographer reporting X-ray examinations requested by A&E was associated with it 12% (p = 0.050) increase in the number of A&E examinations reported and it 37% (p

Live cell imaging of heavy-ion-induced radiation responses by beamline microscopy

To study the dynamics of protein recruitment to DNA lesions, ion beams can be used to generate extremely localized DNA damage within restricted regions of the nuclei. This inhomogeneous spatial distribution of lesions can be visualized indirectly and rapidly in the form of radiation-induced foci using immunocytochemical detection or GFP-tagged DNA repair proteins. To analyze faster protein translocations and a possible contribution of radiation-induced chromatin movement in DNA damage recognition in live cells, we developed a remote-controlled system to obtain high-resolution fluorescence images of living cells during ion irradiation with a frame rate of the order of seconds. Using scratch replication labeling, only minor chromatin movement at sites of ion traversal was observed within the first few minutes of impact. Furthermore, time-lapse images of the GFP-coupled DNA repair protein aprataxin revealed accumulations within seconds at sites of ion hits, indicating a very fast recruitment to damaged sites. Repositioning of the irradiated cells after fixation allowed the comparison of live cell observation with immunocytochemical staining and retrospective etching of ion tracks. These results demonstrate that heavy-ion radiation-induced changes in sub-nuclear structures can be used to determine the kinetics of early protein recruitment in living cells and that the changes are not dependent on large-scale chromatin movement at short times postirradiation. © 2005 by Radiation Research Society.

A theoretical comparison of two optimization methods for radiofrequency drive schemes in high frequency MRI resonators

In this paper, numerical simulations are used in an attempt to find optimal Source profiles for high frequency radiofrequency (RF) volume coils. Biologically loaded, shielded/unshielded circular and elliptical birdcage coils operating at 170 MHz, 300 MHz and 470 MHz are modelled using the FDTD method for both 2D and 3D cases. Taking advantage of the fact that some aspects of the electromagnetic system are linear, two approaches have been proposed for the determination of the drives for individual elements in the RF resonator. The first method is an iterative optimization technique with a kernel for the evaluation of RF fields inside an imaging plane of a human head model using pre-characterized sensitivity profiles of the individual rungs of a resonator; the second method is a regularization-based technique. In the second approach, a sensitivity matrix is explicitly constructed and a regularization procedure is employed to solve the ill-posed problem. Test simulations show that both methods can improve the B-1-field homogeneity in both focused and non-focused scenarios. While the regularization-based method is more efficient, the first optimization method is more flexible as it can take into account other issues such as controlling SAR or reshaping the resonator structures. It is hoped that these schemes and their extensions will be useful for the determination of multi-element RF drives in a variety of applications.

Analysis of cardiac ventricular wall motion based on a three-dimensional electromechanical biventricular model

This paper describes a biventricular model, which couples the electrical and mechanical properties of the heart, and computer simulations of ventricular wall motion and deformation by means of a biventricular model. In the constructed electromechanical model, the mechanical analysis was based on composite material theory and the finite-element method; the propagation of electrical excitation was simulated using an electrical heart model, and the resulting active forces were used to calculate ventricular wall motion. Regional deformation and Lagrangian strain tensors were calculated during the systole phase. Displacements, minimum principal strains and torsion angle were used to describe the motion of the two ventricles. The simulations showed that during the period of systole, (1) the right ventricular free wall moves towards the septum, and at the same time, the base and middle of the free wall move towards the apex, which reduces the volume of the right ventricle; the minimum principle strain (E3) is largest at the apex, then at the middle of the free wall and its direction is in the approximate direction of the epicardial muscle fibres; (2) the base and middle of the left ventricular free wall move towards the apex and the apex remains almost static; the torsion angle is largest at the apex; the minimum principle strain E3 is largest at the apex and its direction on the surface of the middle wall of the left ventricle is roughly in the fibre orientation. These results are in good accordance with results obtained from MR tagging images reported in the literature. This study suggests that such an electromechanical biventricular model has the potential to be used to assess the mechanical function of the two ventricles, and also could improve the accuracy ECG simulation when it is used in heart torso model-based body surface potential simulation studies.

Cost of tobacco-related diseases, including passive smoking, in Hong Kong

Background: Costs of tobacco-related disease can be useful evidence to support tobacco control. In Hong Kong we now have locally derived data on the risks of smoking, including passive smoking. Aim: To estimate the health-related costs of tobacco from both active and passive smoking. Methods: Using local data, we estimated active and passive smoking-attributable mortality, hospital admissions, outpatient, emergency and general practitioner visits for adults and children, use of nursing homes and domestic help, time lost from work due to illness and premature mortality in the productive years. Morbidity risk data were used where possible but otherwise estimates based on mortality risks were used. Utilisation was valued at unit costs or from survey data. Work time lost was valued at the median wage and an additional costing included a value of US$1.3 million for a life lost. Results: In the Hong Kong population of 6.5 million in 1998, the annual value of direct medical costs, long term care and productivity loss was US$532 million for active smoking and US$156 million for passive smoking; passive smoking accounted for 23% of the total costs. Adding the value of attributable lives lost brought the annual cost to US$9.4 billion. Conclusion: The health costs of tobacco use are high and represent a net loss to society. Passive smoking increases these costs by at least a quarter. This quantification of the costs of tobacco provides strong motivation for legislative action on smoke-free areas in the Asia Pacific Region and elsewhere.

Measurement of action spectra of light-activated processes

We report on a new experimental technique suitable for measurement of light-activated processes, such as fluorophore transport. The usefulness of this technique is derived from its capacity to decouple the imaging and activation processes, allowing fluorescent imaging of fluorophore transport at a convenient activation wavelength. We demonstrate the efficiency of this new technique in determination of the action spectrum of the light mediated transport of rhodamine 123 into the parasitic protozoan Giardia duodenalis. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Does chemotherapy improve survival in high-risk Stage I and II Merkel cell carcinoma of the skin?

Purpose: The effectiveness of synchronous carboplatin, etoposide, and radiation therapy in improving survival was evaluated by comparison of a matched set of historic control subjects with patients treated in a prospective Phase II study that used synchronous chemotherapy and radiation and adjuvant chemotherapy. Patients and Methods: Patients were included in the analysis if they had disease localized to the primary site and nodes, and they were required to have at least one of the following high-risk features: recurrence after initial therapy, involved nodes, primary size greater than 1 cm, or gross residual disease after surgery. All patients who received chemotherapy were treated in a standardized fashion as part of a Phase II study (Trans-Tasman Radiation Oncology Group TROG 96:07) from 1997 to 2001. Radiation was delivered to the primary site and nodes to a dose of 50 Gy in 25 fractions over 5 weeks, and synchronous carboplatin (AUC 4.5) and etoposide, 80 mg/m(2) i.v. on Days 1 to 3, were given in Weeks 1, 4, 7, and 10. The historic group represents a single institution's experience from 1988 to 1996 and was treated with surgery and radiation alone, and patients were included if they fulfilled the eligibility criteria of TROG 96:07. Patients with occult cutaneous disease were not included for the purpose of this analysis. Because of imbalances in the prognostic variables between the two treatment groups, comparisons were made by application of Cox's proportional hazard modeling. Overall survival, disease-specific survival, locoregional control, and distant control were used as endpoints for the study. Results: Of the 102 patients who had high-risk Stage I and II disease, 40 were treated with chemotherapy (TROG 96:07) and 62 were treated without chemotherapy (historic control subjects). When Cox's proportional hazards modeling was applied, the only significant factors for overall survival were recurrent disease, age, and the presence of residual disease. For disease-specific survival, recurrent disease was the only significant factor. Primary site on the lower limb had an adverse effect on locoregional control. For distant control, the only significant factor was residual disease. Conclusions: The multivariate analysis suggests chemotherapy has no effect on survival, but because of the wide confidence limits, a chemotherapy effect cannot be excluded. A study of this size is inadequately powered to detect small improvements in survival, and a larger randomized study remains the only way to truly confirm whether chemotherapy improves the results in high-risk MCC. (c) 2006 Elsevier Inc.

Transient temperature rise in a mouse due to low-frequency regional hyperthermia

A refined nonlinear heat transfer model of a mouse has been developed to simulate the transient temperature rise in a neoplastic tumour and neighbouring tissue during regional hyperthermia using a 150 kHz inductive coil. In this study, we incorporate various bio-energetic enhancements to the heat transfer equation and numerical validations based on experimental findings for the mouse, in terms of nonlinear metabolic heat production, homeothermy, blood perfusion parameters, thermoregulation, psychological and physiological effects. The discretized bio-heat transfer equation has been validated with the commercial software FEMLAB on a canonical multi-sphere object before applying the scheme to the inhomogeneous mouse voxel phantom. The time-dependent numerical results of regional hyperthermia of mouse thigh have been compared with the available experimental temperature results with only a few small disparities. During the first 20 min of local unfocused heating, the temperature in the tumour and the surrounding tissue increased by around 7.5 degrees C. The objective of this preliminary study was to develop a validated electrothermal numerical scheme for inductive hyperthermia of a small mammal with the intention of expanding the model into a complete numerical solution involving ferromagnetic nanoparticles for targeted heating of tumours at low frequencies. In addition, the numerical scheme herein could assist in optimizing and tailoring of focused electromagnetic fields for hyperthermia.

Whole brain irradiation following surgery or radiosurgery for solitary brain metastases: Mature results of a prematurely closed randomized Trans-Tasman Radiation Oncology Group trial (TROG 98.05)

We evaluated the effect of adjuvant whole brain irradiation (WBI) after surgery or radiosurgery for solitary brain metastases in a Phase III multicentre trial with randomization to 30-36 Gy WBI or observation. The study was closed early due to slow accrual after 19 patients (WBI 10, observation 9). There was no difference in CNS failure-free survival or overall survival between the arms. There was a trend to reduced CNS relapse with WBI (30% versus 78%, P = 0.12). Limited analysis of quality of life and neurocognitive function data revealed no evidence of difference between the arms. Our results are not inconsistent with two larger randomized trials and support the use of upfront WBI to decrease brain recurrence in this setting. (c) 2006 Elsevier Ireland Ltd. All rights reserved.

Evidence of altered prefrontal-thalamic circuitry in schizophrenia: An optimised diffusion MRI study

MRI diffusion tensor imaging (DTI), optimized for measuring the trace of the diffusion tensor, was used to investigate microstructural changes in the brains of 12 individuals with schizophrenia compared with 12 matched control subjects. To control for the effects of anatomic variation between subject groups, all participants' diffusion images were non-linearly registered to standard anatomical space. Significant statistical differences in mean diffusivity (MD) measures between the two groups were determined on a pixel-by-pixel basis, using Gaussian random field theory. We found significantly elevated MD measures within temporal, parietal and prefrontal cortical regions in the schizophrenia group (P > 0.001), especially within the medial frontal gyrus and anterior cingulate. The dorsal medial and anterior nucleus of the thalamus, including the caudate, also exhibited significantly increased MD in the schizophrenia group (P > 0.001). This study has shown for the first time that MD measures offer an alternative strategy for investigating altered prefrontal-thalamic circuitry in schizophrenia. (c) 2006 Elsevier Inc. All rights reserved.

Prospective Estimation of Radiation Dose and Image Quality for Optimized CT Performance

X-ray computed tomography (CT) is a non-invasive medical imaging technique that generates cross-sectional images by acquiring attenuation-based projection measurements at multiple angles. Since its first introduction in the 1970s, substantial technical improvements have led to the expanding use of CT in clinical examinations. CT has become an indispensable imaging modality for the diagnosis of a wide array of diseases in both pediatric and adult populations [1, 2]. Currently, approximately 272 million CT examinations are performed annually worldwide, with nearly 85 million of these in the United States alone [3]. Although this trend has decelerated in recent years, CT usage is still expected to increase mainly due to advanced technologies such as multi-energy [4], photon counting [5], and cone-beam CT [6].

Despite the significant clinical benefits, concerns have been raised regarding the population-based radiation dose associated with CT examinations [7]. From 1980 to 2006, the effective dose from medical diagnostic procedures rose six-fold, with CT contributing to almost half of the total dose from medical exposure [8]. For each patient, the risk associated with a single CT examination is likely to be minimal. However, the relatively large population-based radiation level has led to enormous efforts among the community to manage and optimize the CT dose.

As promoted by the international campaigns Image Gently and Image Wisely, exposure to CT radiation should be appropriate and safe [9, 10]. It is thus a responsibility to optimize the amount of radiation dose for CT examinations. The key for dose optimization is to determine the minimum amount of radiation dose that achieves the targeted image quality [11]. Based on such principle, dose optimization would significantly benefit from effective metrics to characterize radiation dose and image quality for a CT exam. Moreover, if accurate predictions of the radiation dose and image quality were possible before the initiation of the exam, it would be feasible to personalize it by adjusting the scanning parameters to achieve a desired level of image quality. The purpose of this thesis is to design and validate models to quantify patient-specific radiation dose prospectively and task-based image quality. The dual aim of the study is to implement the theoretical models into clinical practice by developing an organ-based dose monitoring system and an image-based noise addition software for protocol optimization.

More specifically, Chapter 3 aims to develop an organ dose-prediction method for CT examinations of the body under constant tube current condition. The study effectively modeled the anatomical diversity and complexity using a large number of patient models with representative age, size, and gender distribution. The dependence of organ dose coefficients on patient size and scanner models was further evaluated. Distinct from prior work, these studies use the largest number of patient models to date with representative age, weight percentile, and body mass index (BMI) range.

With effective quantification of organ dose under constant tube current condition, Chapter 4 aims to extend the organ dose prediction system to tube current modulated (TCM) CT examinations. The prediction, applied to chest and abdominopelvic exams, was achieved by combining a convolution-based estimation technique that quantifies the radiation field, a TCM scheme that emulates modulation profiles from major CT vendors, and a library of computational phantoms with representative sizes, ages, and genders. The prospective quantification model is validated by comparing the predicted organ dose with the dose estimated based on Monte Carlo simulations with TCM function explicitly modeled.

Chapter 5 aims to implement the organ dose-estimation framework in clinical practice to develop an organ dose-monitoring program based on a commercial software (Dose Watch, GE Healthcare, Waukesha, WI). In the first phase of the study we focused on body CT examinations, and so the patient’s major body landmark information was extracted from the patient scout image in order to match clinical patients against a computational phantom in the library. The organ dose coefficients were estimated based on CT protocol and patient size as reported in Chapter 3. The exam CTDIvol, DLP, and TCM profiles were extracted and used to quantify the radiation field using the convolution technique proposed in Chapter 4.

With effective methods to predict and monitor organ dose, Chapters 6 aims to develop and validate improved measurement techniques for image quality assessment. Chapter 6 outlines the method that was developed to assess and predict quantum noise in clinical body CT images. Compared with previous phantom-based studies, this study accurately assessed the quantum noise in clinical images and further validated the correspondence between phantom-based measurements and the expected clinical image quality as a function of patient size and scanner attributes.

Chapter 7 aims to develop a practical strategy to generate hybrid CT images and assess the impact of dose reduction on diagnostic confidence for the diagnosis of acute pancreatitis. The general strategy is (1) to simulate synthetic CT images at multiple reduced-dose levels from clinical datasets using an image-based noise addition technique; (2) to develop quantitative and observer-based methods to validate the realism of simulated low-dose images; (3) to perform multi-reader observer studies on the low-dose image series to assess the impact of dose reduction on the diagnostic confidence for multiple diagnostic tasks; and (4) to determine the dose operating point for clinical CT examinations based on the minimum diagnostic performance to achieve protocol optimization.

Chapter 8 concludes the thesis with a summary of accomplished work and a discussion about future research.